A communications network may be characterized as “connection-oriented” or “connectionless.” A connection-oriented network is conceptually similar to a telephone network. First, a source entity opens a connection using a call-setup protocol to create a circuit with a destination entity. Using the connection, the source entity transmits data to the destination entity, which receives the data in the order it is transmitted. The bandwidth associated with this connection is reserved while the connection is open and is therefore unavailable for other connections, even if the circuit is idle.
Due to this bandwidth reservation requirement, connection-oriented networks are ill-suited to carry bursty data communications. The bandwidth of a connection is wasted when it idles between bursts of communications and, when the network is congested, idle bandwidth reserved for other connections typically cannot be commandeered to alleviate the congestion.
In contrast, the transmission of data over a connectionless network is analogous to sending parcels through the mail: each packet of data on the network is labeled with a destination address and processed independently of any other packet sent across the network. The bandwidth associated with a connectionless link is not reserved and may be allocated to other entities on a first-come, first-served basis. This routing model permits the efficient use of network resources since bursty data traffic only uses bandwidth as needed and, in congestion scenarios, packets may be dropped if network resources (such as buffer memory) become full. The Internet carries data according to the connectionless model using a packet-based protocol called “internet protocol” (IP).
A problem arises when an application requires data transfer with a guaranteed minimum quality-of-service (QoS) using a connectionless network such as the Internet or a private packet-based network. For example, a source entity transmitting data associated with voice, videoconferencing, or other real-time communications applications may require that all the data packets it sends arrive in order in a relatively-constant, predetermined time frame. In this case, the same routing flexibility that permits the efficient use of network resources on the connectionless network also hinders the provision of a guaranteed QoS, as packets sent over the network may arrive out of order, may arrive late, or not arrive at all. Therefore, there is a need for techniques that facilitate the provision of a guaranteed QoS over a typical connectionless network.